1. Field of the Invention
The present invention relates generally to a color cathode ray tube, and more particularly to a color cathode ray tube capable of reducing heat damage that occurs during heat treatment, while at the same time enhancing productivity by improving a structure of skirt seal edges of a flat panel.
2. Description of the Background Art
FIG. 1 is a partial sectional view showing a structure of a general color cathode ray tube (CRT).
Referring to FIG. 1, as a main element for realizing pictures in a picture display apparatus such as a television receiver or a computer monitor, a color CRT generally comprises a panel 1 arranged in the front of the color CRT and a funnel 2 arranged in the rear of the panel 1.
In addition, in an inner space formed by the panel 1 and the funnel 2, the color CRT further includes a fluorescent screen 4 for emitting light, an electron gun provided within a neck portion of the funnel 2 for projecting an electron beam 6 for emitting light from the fluorescent screen 4, a shadow mask 3 for selecting color so that light is emitted from the fluorescent screen 4, a frame assembly including a main frame 7 for applying tension to the shadow mask 3 and a sub frame 13 for supporting the shadow mask 3, a spring 9 provided at a side face of the main frame 7 for coupling the frame assembly 7 to the panel 1, an inner shield 8 welded and fixed to the sub frame 13 for shielding an external earth magnetic field, and a reinforcement band 12 provided at an outer face of a skirt of the panel 1 for dispersing stress given to the CRT in a state of high vacuum and securing impact-resistant performance.
In addition, the outside the neck of the funnel 2 is provided with a deflection yoke 5 for deflecting the electron beam 6 projected from the electron gun (not shown) in various directions, i.e., up, down, left and right and 2, 4 and 6-pole magnets for correcting a traveling locus of the projected electron beam 6 so that the projected electron beam 6 precisely strikes a prescribed fluorescent substance for the purpose of preventing staining, which affects color purity.
Processes for manufacturing the color CRT generally comprising a glass (the panel and funnel), the shadow mask, the electron gun, the fluorescent screen, the deflection yoke, etc. as shown in the above, and will now be briefly explained below.
The processes include a shadow mask assembly process, a black matrix (BM) process and a phosphor (PH) application process for repeatedly performing a clean, an application, a dry, an exposure, and a development of the shadow mask such that pixels conforming to a particular specification are formed, an aluminum deposition process for depositing aluminum on a panel to which a fluorescent substance is applied, a panel baking process for passing an assembly as a combination of the panel and the shadow mask and carried on a panel holder through a stabilizing furnace or a panel baking furnace in order to eliminate internal stress of the panel and the shadow mask, a frit process for making a bulb by welding the panel and the shadow mask to a funnel to which frit glass is applied, an enclosure process for inserting an electron gun into a funnel neck of the bulb, and an exhaust process for placing the bulb into a state of high vacuum using a rotary pump and a diffusion pump while the bulb passes through a high-temperature furnace and for discharging gas filled in electrodes and dissolving a cathode by removing the occlusion and absorption gases in the bulb.
On the other hand, in connection with a recent trend of size enlargement and flatness of the color CRT, there is a significant problem in the aforementioned manufacture processes of the CRT, particularly, the frit process in which the panel is welded to the funnel. For example, when the frit having a property of melt and recrystallization at high temperature is applied to the welding portion of the panel to the funnel, the frit does not provide a complete enclosure to seal the surfaces of the panel and the funnel and flows down around the funnel (see FIG. 10a). When the frit flows down around the funnel due to its low viscosity, an acute angle and a droop of the frit are generated causing a crack in the bulb.
The shape of the frit applied to the welding portion of the panel and the funnel and bubbles formed within the frit are responsible for cracks caused by heat stress and vacuum stress. A main reason for the shape and the bubbles is the steep flow of the frit.
The reason for such a steep flow of the frit is mainly due to the trend of size enlargement and flatness of the color CRT. Namely, the frit has steep flow because the panel whose outer surface is flat (see FIG. 2b) has a structure in which the weight of the panel increases due to the enlargement and flatness of the CRT, thus creating the enlargement and flatness of the panel.
Herein, when the frit is recrystallized, the flow of the frit on the welding portion of the panel and the funnel increases due to the increased weight of the panel. Therefore, the panel (after recrystallization) of the frit has a shape different from a general shape under the same conditions, i.e., a high fin shape.
Typically, the weight of the flat panel (see FIG. 2b) is increased over a curved panel (see FIG. 2a). As a result, the force of the panel that presses against the funnel in a frit sealing furnace is increased, thus changing the flow of the frit. Since much of the frit flows down around the seal surface of the funnel due to insufficient time for the frit to cover the seal surface of the panel and the relative increase of the force pressing on the panel, an acute angle (the source of the crack of the panel) is formed at the end portion of the seal surface of the panel.
Particularly, the recent trend of size enlargement and flatness of current panels leads to an increase in the thickness of the panel, making it heavier, which gives rise to the significant problem of the bulb crack.
To overcome such a problem, a furnace schedule should be changed. However, when such a change is made, there arises the more significant problem of reduction in the quantity of products, i.e., product index, for the CRT.